Electric motors, such as three-phase, two-phase and DC motors, when once installed, often rotate in a predetermined direction of rotation. In many installations and applications, it is essential that the predetermined direction of rotation be maintained and that there should be no occurrence of rotation in the reverse direction. When the direction of rotation is inadvertently reversed, there is the potential damage to the driven equipment and may even be hazardous to those riding in or upon a conveyance driven by these motors.
It is not uncommon for power interruptions to occur in power distribution systems. At the end of these power interruptions, when the power is restored, the phase or polarity is sometimes reversed through the inadvertent transposition or interchangement of the input wires.
In three-phase systems, a reversal in motor direction occurs when any two of three power lines are interchanged. In a two-phase system, a change of motor direction occurs when either pair, the reference or quadrature power lines, are transposed. In a DC power system, such reversal of motor direction occurs when the polarity of the input power lines is interchanged.
As such, in three-phase or two phase applications, such phase reversals can also occur when a power distribution transformer is removed or replaced in local repair or maintenance. Accidental reversals of phase or polarity can also occur in larger facilities, such as steel mills, automotive assembly and production plants, when maintenance electricians or maintenance personnel are installing or replacing other equipment along a production stream.
Equipment that is sensitive to the reversal of the direction of rotation include conveyers, both belt and overhead, escalators, people movers, elevators and other conveyance equipment. Severe damage can result when the direction of rotation is inadvertently reversed; serious injuries to persons being transported can be the result of such reversal. In the case of conveyers for use in assembly operations, serious physical damage to the product and tooling can occur during such an event.
Motor reversal protection can also be effective in equipment such as hydraulic pumps, air compressors, production punch presses, and the like. When the direction of rotation of these pieces of equipment are reversed, serious physical damage can occur, which would result in long down times, as well as, increased repair or replacement costs.
There are several U.S. Patents that disclose phase reversal switch mechanisms, one of which one that teaches of a power switching device; another teaches of three phase reversal protection. They are and include:
U.S. Pat. No. 4,357,502, granted Nov. 2, 1982, to H. R. Beck, discloses a three-phase, phase reversal switch assembly which is driven by an actuation device to provide a rectilinear motion that applies torque to a rotatable mechanism. A second device engages is a shift mechanism that operates a shift link to engage torque transmission to one or the other reversal mechanisms. The means for actuating the switch and shift actuators are not disclosed, nor is the any means of phase sequence detection.
U.S. Pat. No. 4,045,682, granted Aug. 30, 1977, to C. R. Poorbaugh, et al, discloses a three-phase fractional horsepower motor having a specialized cam plate, its rotary position being sensed by microswitches to control the activation of a solenoid driven motor contactor. The system as disclosed by Poorbough, et al, teaches that when the phase is reversed, that it is impossible to start the three phase motor. It does not attempt to correct for a reversed phase condition and requires that the cam plate be manually repositioned to reset the device to restore electrical service to the attached equipment.
U.S. Pat. No. 3,673,426, granted Jun. 27, 1972, to D. E. Weston, et al, teaches of a three-phase switch that is primarily used for selectively connecting an electrical rotary machine to a power distribution system for use as a generator to supply power to the system or for use as a motor that is drawing power from the system.
Accordingly, it is an object of the present invention to provide an apparatus that is responsive to the phase sequence of the power lines connected to a three-phase motor such that the motor will operate in a unidirectional manner.
It is another object of the present invention to provide an apparatus that is responsive to the phase sequence of the power lines connected to a three-phase motor that will prevent a three-phase motor to operate in the reverse direction of rotation.
It is still another object of the present invention to provide an apparatus that is responsive to the phase sequence of the power lines connected to a three-phase motor that will prevent a three-phase motor and its driven load to operate in the reverse direction of rotation.
It is still yet another object of the present invention to provide an apparatus that is responsive to the phase sequence of the power lines connected to a three-phase motor that will automatically prevent a three-phase motor and its driven load to operate in the reverse direction of rotation without the necessity of being reset upon detection of a phase reversal.
An additional object of the present invention is to provide an apparatus that is responsive to the phase sequence of the power lines connected to a three-phase motor that will automatically protect a driven load to operate in the reverse direction of rotation.
Still, an additional object of the present invention is to provide an apparatus that is responsive to the phase sequence of the power lines in a two-phase power distribution system, connected to a two-phase motor that will automatically prevent the two-phase motor and its driven load to operate in the reverse direction of rotation without the necessity of being reset upon detection of a polarity reversal.
A final object of the present invention is to provide an apparatus that is responsive to the polarity of the power lines connected to a DC motor that will automatically prevent a DC motor and its driven load to operate in the reverse direction of rotation without the necessity of being reset upon detection of a polarity reversal.
These and other objects and advantages of the present invention will be better appreciated and understood upon reading the following detailed description, when taken in conjunction with the attached accompanying drawings.